Those are the 79” side rails for a metal hook-in bed frame (or an adjustable metal bed support system designed to work with a wooden headboard and footboard).
Key Features & Identification:
* Overall Length (~79 inches / 6’7”):
Standard mattress lengths for Full (75"), Queen (80"), and King (80") beds fall right in this range. A 79-inch length is typical for Queen or King size side rails.
* Attachment Clamps / Brackets:
The perpendicular metal brackets mounted to the main L-angle rails are designed to clamp onto cross-support bars or fit into the slot/hook receivers of a headboard and footboard.
* Center Support Legs & Glide Feet:
The three vertical drop legs extending downward on each rail feature white/adjustable plastic glide feet at the bottom.
* Frames designed for Queen, King, or California King setups utilize 6 total legs (3 per side rail) to support the weight of a heavy box spring and mattress without sagging in the middle.